==== Intro to Data Core ====

Their 340-day mission aboard the International Space Station (ISS) is twice the length of a normal stay.

Their extended tour is part of an effort to study the effects of long-duration spaceflight on the body.


=== Installing Data Core ===

But scientists will gain further insights by comparing Scott Kelly with his Earthbound identical twin, Mark.

A Soyuz capsule carrying Kelly, Kornienko and Russian crew member Sergey Volkov parachuted down on to a steppe in 

Kazakhstan at 10:26 local time (04:26 GMT).


==== Data Sources =====

The mission is a record for the ISS and will give Cmdr Kelly a tally of 520 cumulative days in space, over four flights.

=== Event Sinks ===

Cmdr Kelly has also returned rocket (salad) seeds that were taken up to the orbiting outpost by UK astronaut Tim Peake in December. 

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They will be distributed to schools to allow pupils to compare their growth with rocket plants that have stayed on Earth.